Guidelines to Drive User Adoption of SharePoint
SharePoint Advisor magazine has an excellent article by Garry Smith that covers the most important aspect of a SharePoint deployment: getting people to use it.
After you have a solid start on the structure and a plan to migrate documents, you need a plan to encourage people to continue participation. So I'll add one element to Gary's structured approach: a rewards system. Rewards can range from a "top contributors" section on the home page, to a certificate, to a night out, and can be awarded based on quantity, peer-ratings or votes. Champions are great at coming up with the specifics, the point is to address it.
Why do we need rewards systems? Most people do not learn to work in open, collaborative, sharing environments. Before we learn how to function as a team, we function as individuals. As individuals there will always be tendencies to stockpile knowledge and work in isolation. It is natural to put self-preservation before the common good. To do otherwise is an acquired trait, and it needs to be encouraged before people can experience the benefits and do it spontaneously. Experience leads to internalization. So find ways to encourage participation and get everyone contributing to a truly living hub. Evolve your team.
And check out Garry's article.